Many conventional laundry machines use a complex mechanism which adapts a constant speed motor, e.g., one which runs at approximately 1800 RPM, to the comparatively slow back-and-forth motion of an agitator during a wash cycle. The same mechanism adapts the motor to a unidirectional spin cycle during which a tub rotates alone or together with the agitator, at a speed which may be in the order of 600 RPM. The physical dimensions of the motor required for such machines, as well as the dimensions of a transmission for coupling the motor to the machine, is relatively large, and may necessitate the motor being positioned a considerable distance from, and out of line with, the axis of the drive shaft of the laundry machine. This distance must be sufficiently large to accommodate an intermediate belt transmission, and related pulleys, as well as whatever gearing is required to step down the speed of the motor. In addition, a transmission clutch is provided to transition the machine from the slow agitate motion to the high unidirectional spin speed.
Such a mechanical arrangement is unbalanced necessitating special measures to restore the balance of the machine. Further, because of severe demands made on such a machine, particularly on the transmission during a reversal of direction, some of such machines may have a relatively short life. The above discussed factors tend to increase the initial cost of such machine, as well as maintenance costs.
In addition, the range of operations of conventional laundry machines is, by necessity, limited. Providing such machines with the capability of handling a larger number of different laundry conditions, such as may be presented by the variety of present day fabrics and wash loads, increases the complexity of the transmission as well as the overall cost of the machine. Thus, the capability of such conventional laundry machines represents a compromise between different expected laundry conditions, modified by cost and mechanical considerations.
It is also important to minimize the noise, vibration and pulsations of a household washing machine not only to increase the life and reliability of the machine, but also to improve the environmental impact of such disruptions.
To overcome the aforementioned shortcomings, adjustable speed drives comprising electronically commutated motors (ECMs) for use in laundering machines have been developed. One such device is disclosed in U.S. Pat. No. 4,556,827 issued Dec. 3, 1985 to David M. Erdman and assigned to the same assignee as the subject invention. The laundering apparatus of that patent includes an electronically commutated motor. Although electronically commutated motors reduce the complexity, size and cost of laundering apparatus, and minimize or overcome many of the above problems, it is desirable to reduce these factors even further. The present invention, therefore, utilizes a switched reluctance motor (SRM) drive system for operating laundering apparatus. In contrast to an ECM, an SRM requires no permanent magnets and no rotor windings.
In addition, the SRM is directly operable to cover a broad range of speed and related torques without switching or relay means to change motor connections, and may be provided with position sensing circuits that are operative down to zero speed.
A switched reluctance motor and its associated drive system including a method for indirectly estimating rotor position in an SRM drive system is disclosed in U.S. Pat. No. 4,772,839, issued Sept. 20, 1988 to S. R. MacMinn and P. B. Roemer and in copending patent application Ser. No. 07/332,205 filed by S. R. MacMinn et al on Apr. 3, 1989, both of which are assigned to the same assignee as the subject invention, and both of which are hereby incorporated by reference.